Here are some pictures of an electric tracing attachment I built in about early 2002.
I was wanting to create formers for metal spinning in metal and didn't want to do it
manually. A hydraulic tracing attachment would be great but the cost couldn't be justified
and the lathe pictured being a Kerry 1140 would have made the search harder or required 
modifications to the tracer. I realised that as it didn't need it to do sqaure shoulders
some system of driving the cross slide while the longitudinal feed was running would do
the job. Originally a fancy quill was envisaged to contact the pattern and the output would 
be feed to the servo controller. I decided in the end to get on with the metal spinning and
not the tracer so the set-up shown here is crude but functional for what I required. The 
controller was based around the servo controller shown in National semiconductor LM675 
power op-amp datasheet. This was chosen due to single supply rail requirement, 3A rating 
, current limiting and thermal protection. Normally for a servo controller one pot is used 
to set the required position and the other for position feedback. In this case one is set 
in centre position and the other slightly off centre so the controller drives the cross slide 
towards the pattern.  The rate can be altered by the difference between to 2 pot settings. 
Across the feedback pots centre and one outer leg another pot is attached and one wire 
routed via the stylus and pattern so that when the stylus touches the pattern the servo 
controller will drive the cross slide out. This hunts in and out but provided very acceptable
results for what was required and didn't cost much. The servo controller was powered by a 12V 
car battery. Care needed to be taken to keep swarf from shorting the pattern to holder or 
stylus to cross slide as this made it keep going toward the pattern and cut dramatically into 
the work piece. Cuts were controlled primarilly with the compound slide after suitable 
positioning of the stylus.

electrictracer1.jpg	this shows the pattern holder bar which clamps to the lathe bed. The 
			pattern is electrically isolated from the holder. The follower stylus 
			1.6mm (1/16") welding rod can be seen as is also isolated from the 
			lathe.
 
electrictracer2.jpg	the controller is based on the servo controller shown in National
			semiconductor LM675 datasheet application suggestions.

electrictracer3.jpg	wiper motor fixed to end of carriage where suitable fixing holes 
			already existed. The cross slide handle has been replaced. The one
			shown has a tooth belt wheel mounted and can rotate freely until 
			the round pin is engaged when tracing is wanted.

electrictracer4.jpg	bowl former and template. This former has not been touched after
			tracing.

electrictracer5.jpg	tankard former and template. This has most definately been touched
			after tracing.

electrictracer6.jpg	spun items from formers.

D Billington 16/11/2004 djb@djbillington.freeserve.co.uk